pgsql: Change "long" numGroups fields to be Cardinality (i.e., double).

Change "long" numGroups fields to be Cardinality (i.e., double).

We've been nibbling away at removing uses of "long" for a long time,
since its width is platform-dependent.  Here's one more: change the
remaining "long" fields in Plan nodes to Cardinality, since the three
surviving examples all represent group-count estimates.  The upstream
planner code was converted to Cardinality some time ago; for example
the corresponding fields in Path nodes are type Cardinality, as are
the arguments of the make_foo_path functions.  Downstream in the
executor, it turns out that these all feed to the table-size argument
of BuildTupleHashTable.  Change that to "double" as well, and fix it
so that it safely clamps out-of-range values to the uint32 limit of
simplehash.h, as was not being done before.

Essentially, this is removing all the artificial datatype-dependent
limitations on these values from upstream processing, and applying
just one clamp at the moment where we're forced to do so by the
datatype choices of simplehash.h.

Also, remove BuildTupleHashTable's misguided attempt to enforce
work_mem/hash_mem_limit.  It doesn't have enough information
(particularly not the expected tuple width) to do that accurately,
and it has no real business second-guessing the caller's choice.
For all these plan types, it's really the planner's responsibility
to not choose a hashed implementation if the hashtable is expected
to exceed hash_mem_limit.  The previous patch improved the
accuracy of those estimates, and even if BuildTupleHashTable had
more information it should arrive at the same conclusions.

Reported-by: Jeff Janes <jeff.janes@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/CAMkU=1zia0JfW_QR8L5xA2vpa0oqVuiapm78h=WpNsHH13_9uw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8f29467c57f44cc2cdd9e4e53c6ab1b07375d5b4

Modified Files
--------------
src/backend/executor/execGrouping.c       | 36 ++++++++++++++++---------------
src/backend/executor/nodeAgg.c            | 30 ++++++++++++++------------
src/backend/executor/nodeRecursiveunion.c |  1 -
src/backend/executor/nodeSetOp.c          |  1 -
src/backend/executor/nodeSubplan.c        | 19 +++++++---------
src/backend/optimizer/path/costsize.c     | 26 ----------------------
src/backend/optimizer/plan/createplan.c   | 26 ++++++----------------
src/include/executor/executor.h           |  2 +-
src/include/nodes/plannodes.h             |  6 +++---
src/include/optimizer/optimizer.h         |  1 -
src/include/optimizer/planmain.h          |  2 +-
11 files changed, 55 insertions(+), 95 deletions(-)